(1) Field of the Invention
The present invention relates to fabrication processes used to create a dynamic random access memory, (DRAM), device, on a semiconductor substrate, and more specifically, relates to a process used to create a crown shaped, storage node structure, for the DRAM device.
(2) Description of Prior Art
Cylindrical shaped, or crown shaped, capacitor structures, have been used to increase the surface area of DRAM capacitors, and thus increase the signal or performance of DRAM devices. Stacked capacitor structures, (STC), located overlying the transfer gate transistor, of the DRAM device, are limited by the dimensions of the underlying transfer gate transistor. Therefore to increase the surface area of the STC structure, without infringing on neighboring, underlying transfer gate transistors, specific STC shapes are employed. For example, a crown shaped, storage node structure, comprised of vertical polysilicon features, connected to an underlying horizontal polysilicon feature, offers increased storage node surface area, when compared to counterparts, fabricated without vertical polysilicon features, or without the use of the crown shape. The use of the crown shaped, STC structure, however results in a process difficulties when creating the crown shaped, storage node structure. For example after creating an opening, in a thick insulator layer, a polysilicon layer is deposited, on the top surface of the thick insulator layer, as well as on the surfaces of the thick insulator layer, exposed in the opening. Removal of the polysilicon layer, from the top surface of the thick insulator layer, results in a crown shaped, polysilicon structure, comprised of vertical polysilicon features, on the sides of the opening in the thick insulator layer, connected to a horizontal polysilicon feature, residing at the bottom of the opening in the thick insulator layer. However difficulties can occur during the removal of polysilicon, from the top surface of the thick insulator layer, specifically, redeposition of material on, or damage to, the resulting crown shaped, polysilicon structure, residing in the opening in the thick insulator layer.
A method used to alleviate the difficulties of polysilicon removal, in the presence of the crown shaped, polysilicon structure, is to protect the crown shaped, polysilicon structure, located in the opening in the thick insulator layer, via filling the opening with either spin on glass, (SOG), or photoresist, than removing these fill layers, after removal of unprotected polysilicon, located on the top surface of the thick insulator layer. Ying, in U.S. Pat. No. 5,753,547, describes a SOG fill, as a protective fill, during the crown shaped, polysilicon definition procedure, however the additional cost of depositing SOG, and then planarizing it back, via plasma etch procedures, to expose polysilicon, is not attractive. Ajika et al, in U.S. Pat. No. 5,597,755, teach a photoresist fill, for protection of the crown shaped structure, during the polysilicon removal process. However this patent also employs a costly etch back procedure to expose the polysilicon to be removed. This invention will also describe a procedure in which a photoresist plug will be used as protection for the subsequent crown shaped, polysilicon structure, during removal of polysilicon from the top surface of a thick insulator layer. However unlike the prior art, the photoresist plug is planarized using a novel photoresist exposure--development procedure, avoiding the costly plasma etch back procedure.